Plasticized rubber compositions and method of plasticizing rubber



. rubber.

' phosphine halide and retene.

her is used in the present specification and at-' Patented Dec. 5, 1944 PLASTICIZED RUBBER COMPOSITIONS AND METHOD OF PLASTICIZING RUBBER Robert L. Sibley, Nitro. w.va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application February 6, 1942, Serial No. 129,794

Claims.

This invention relates to a method of increasing the plasticity of a rubber and to the new compositions obtained thereby.

It is common practice in the manufacture of rubber articles to add to the rubber during processing a materialwhich decreases the resistance of the rubber to flow thereby facilitating the incorporation of compounding and vulcanizing ingredients and providing a composition amenable to shaping into final form. These additives take the form of lubricants such as pine oil or so called catalytic softeners as for example aromatic mercaptans or conventional plasticizers like dibutyl phthalate which are extensively used with certain synthetic rubbers and permanently alter and modify the properties of the original rubber. While many of the softeners or plasticizers of this invention exhibit a catalytic softening action and perhaps some lubricating action. they are further characterized by the fact that they can be used as conventional plasticizers in amounts which permanently modify and alter the rubber.

In accordance with this invention it has been discovered that the products obtained by treating a rubber with an aryl phosphine halide and a condensed aromatic polynuclear hydrocarbon are valuable agents for increasing the plasticity of a A preferred aspect of the invention contemplates the use of a soft sticky product obtained by treating a natural rubber with an aryl The term a rubtached claims to mean a vulcan zable plastic material which possesses appreciable extensibility under load coupled with the property of forcibly retracting to approximately its original size and shape after the load is removed.

The preparation of the products obtained by treating a rubber with an aryl phosphine nalide and a condensed aromatic polynuclear hydrocarbon is disclosed in co-pendin application of George D. Martin, Serial No. 416,588, filed Octodichlor phosphine of meta diphenyl benzene,

chlor phenyl dichlor phosphine, cymyl dichlor phosphine and retyl dichlor phosphine. Many of the products described in the aforementioned applications are tough plastic materials and where it is desired to produce soft tacky products having enhanced catalytic softening effects the arylphosphine halide can be first treated with the condensed aromatic polynuclear hydrocarbon followed by the addition of the rubber.

While the preparation of the new softening or plasticizing agents is illustrated by typical examples given below, the present invention is not concerned with the preparation of the new adjuvants and is not limited thereto.

Example I Substantially 100 partsby weight of crude tolyl dichlor phosphine (the lower layer obtained, by

reacting toluene with P013 in the presence of anhydrous aluminum chloride as described in Liebigs Annalen, vol. 212, pp. 206, 207, and drawing off the lower layer which separated upon cooling) was added to a carbon disulflde cement containing substantially 100 parts by weight of guayule. The charge was stirred and heated at refluxing temperature for about an hour, 100 parts by weight of technical retene added and the stirring and heating continued for twelve hours after which a Liebig type condenser was substituted for the reflux condenser and the solvent removed by distillation. Heating was continued for a short time after distillation had substantially ceased and then live steam was introduced and after a thorough steaming out, the product was washed with water and dried to constant weight. A soft sticky rubbery product was obtained.

The physical nature of the product makes it somewhat difficult to handle and weigh but where desired it can be blended with an inert diluent to render it less tacky. Carbon black, paraffin, pine tar or starch are suitable for this purpose.

Example II Substantially 100 parts by weight of crude tolyl dichlor phosphine was added to a carbon disulfide cement containing substantially 100 parts by weight of pale crepe rubber. The mixture was heated to refluxing temperature for about minutes and a mixture of oleyl chloride and retene added. The latter was obtained by mix-. ing parts by weight of oleyl chloride with 100 parts by weight of technical retene in the presence of 4 parts by weight of anhydrous aluminum chloride. After the initial vigorous reaction had subsided somewhat as evidenced by an abatement of the KC! evolved, the mixture was added to the rubber cement and the heating continued for twelve hours. The solvent was then removed and the residue washed and dried to constant weight. A soft sticky product was obtained.

Example III Substantially 100 parts by weight of technical retene was dissolved in 200 parts by weight of carbon disulflde and substantially 100 parts by weight of crude tolyl dichlor phosphine added to the solution so prepared. The charge was heated under reflux for about an hour after which a carbon disulflde cement containing '100 parts by weight of crepe rubber was added and the heating continued for twelve hours. The solvent was then removed, the residue washed with water and dried to constant weight. The product, although rubbery, was soft and tacky.

' Example IV Substantially 100 parts by weight of crude tolyl dichlor phosphine was added to a carbon disulflde cement containing substantially 100 parts by weight of pale crepe rubber. The charge was heated at refluxing temperature for about 90 minutes, substantially 100 parts by weight of technical retene added and the heating continued for 24 hours. The solvent was then removed by distillation, the residue treated with steam and washed with water. Since the portion of the product solublein acetone exerts a strong p1as-' ticizing or softening action on rubber, it is preferred to concentrate this active ingredient by extracting the residue remaining after the washing operation, with acetone. Upon subsequent removal of the acetone a waxy solid was'obtained.

Example V Example VI Chlorine was passed into technical retene until-l8 percent by weight of chlorine had been absorbed. 118 parts by weight of this chlorinated retene and 50 parts by weight of crude tolyl dichlor phosphine were added to a benzene cement containing 100 parts by weight of pale crepe rubber. The charge was heated at '70-80 C. for five hours, the solvent removed by distillation and the residue treated with steam, washed with water and dried. A soft tacky product was obtained.

The following specific embodiments of the in- I vention illustrate the desirable propertiesv of the I new softening or plasticizing agents and are not to be taken as limitative of the invention.

A quantity of a rubber-carbon black master batch composed of sixty parts smoked sheets of rubber and forty parts of carbon black was milled for a short time to assure uniformity and then smoked sheets of rubber, compounding and vulcanizing ingredients (except sulfur) were added in such amount as to produce rubber stocks of assess the composition shown below. In order to. assure reproducible results the same temperature and time of milling was employed in the preparation of each stock. Thus the milling time was nine minutes and the mill rollswere maintained at a temperature of 100 C. In this manner, a rubber base stock was compounded comprising Base stock, parts by weight Condensation product p-amino diphenyl and ace 1.5 Mercaptobenzothiazole 0.75

From the base stock so prepared rubber stocks were compounded comprising am What mm m but M 2:52,?

Product of Example 1. 0 Product of Example 1. 5 Product of Example .3! 1.0 Product of Example ..I 1. 5 Product of Example 111... 1. 0 Product of Example III 1. 5 Product of Example IV 1. 0 Product of Example V. 1. 0 Product 0! Example VI 1. 0

At the end of the milling period the stocks so compounded were sheeted out and allowed to stand until they had cooled to room temperature. The sheets were then folded back upon themselves to build up a thickness sufllcient to.cut test pellets and test pellets cut out by means of a suitable die. The plasticity or resistance of the pellets to flow was measured by means of an extrusion plastometer. A description of the method and apparatus-is given by J. H. Dillon in Rubber Chemistry and Technology, volume 9 (1936), pages 496-501. The quantity measured was the time in seconds required to 'extrude a "given volume of rubber at constant temperature and under a constant pressure. In the particular tests herein described the pellets were preheated 18 minutes at 149 C. and then inserted into the plastometer, the latter being maintained as near to 82 C. as possible. With ordinary care the temperature can be kept within the range of 82 to 855' C. The pressure on the plunger was 5.5 pounds per square inch. The figures given in the table below are ratios based upon the control Plasticlty figure Stock stresses? 1 Test pellet preheated 24 minutes at 0., and extruded under 4.5 pounds/in. air pressure.

class of materials exert a powerful catalytic softening action when incorporated into rubber.

Frequently the amount Of the softening agent can be increased with advantageous effects. For example, the preferred materials are useful binding agents and extenders, as well as softeners, for rubber which are exceptionally diflicult to break down and knit on a rubber mill. While vulcanized scrap alone is difncult to form into a smooth sheet, in combination with the preferred materials useful compositions can be readily and easily obtained without resort to a reclaiming process. For example, vulcanizable compositions were easily and quickly compounded irom ingredients comprising Stock Ground truck peels Product of Example I Non-tacky, rubbcr-likecfiroduct obtained by treating ground tru peels with tolyl dichlor phosphine and technical retene Zinc oxide Homogeneous compositions were formed which gave smooth sheets when out from the mill rolls. The stocks so compounded were vulcanized in a press in the usual manner by heating for different periods of time at the temperature of 30 pounds steam pressure per square inch. The modulus and tensileproperties of the cured products were as follows:

Table I Modulus of Cure elasticity in Tensile at Ult. Stock time in lbs/in. at break in elong.

mins. elongation lbs./in. per cent of 200% tained by treating a rubber with an aryl phosphine halide are claimed in co-pending application of Paul M. Downey, Serial No.- 426,069, filed January 8, 1942.

While the specific embodiments furnished to illustrate the invention disclose the addition of ti: 2 plasticizing agent to the rubber on an ordinary rubber mill, other types of apparatus may be used as for example, a Banbury type mixer or a Gordon plasticator.

Again, the invention is not limited to the speciflc embodiments of the invention. ferred materials may be employed in different proportions than specifically shown and in conjunction with other compounding and vulcanizing ingredients. Obviously, many variations can The pre-.

present invention. This invention is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. A composition comprising predominately a rubber and as a softener and plasticizer thereof a heat reaction product of a. rubber and substantial proportions based on the rubber of an aryl phosphine halide having the halogen linked to the phosphorus and an aromatic condensed polynuclear compound.

2. A composition comprising predominately a natural rubber and as a softener and plasticizer thereof a heat reaction product of a rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked .to the phosphorus and an aromatic condensed polynuclear hydrocarbon.

3. A composition comprising predominately v vulcanized crap rubber and as a softener, binder and plasticizer thereof a heat reaction product of a rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked'to the phosphorus and an aromatic condensed polynuclear hydro carbon.

i. A composition comprising predominately a vulcanized ground scrap rubber and as a softener, binder and plasticizer thereof a soft sticky heat reaction product of a natural rubber and substantial proportions based on the rubber of tolyl dichlor phosphine having the two chlorine atoms linked to the phosphorus atom and retene.

5. Unvulcanized india rubber of decreased resistance to flow containing as the softening ingredient a small amount of a soft tacky heat reaction product of a rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked to phosphorus and a condensed polynuclear aromatic hydrocarbon.

6. Unvulcanized india rubber of decreased resistance to flow containing as the softening ingredient a. small amount of a soft sticky heat reaction product of a natural rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked to phosphorus and a condensed polynuclear aromatic hydrocarbon.

7. Unvulcanized india rubber of decreased resistance to flow containing as the softening ingredient a small amount of a soft tacky heat reaction product of guayule rubber and substantial proportions based on the rubber of tolyl dichlor phosphine having the two chlorine atoms [linked to phosphorus and retene. 8. The method of increasing the plasticity of unvulcanized rubber which comprises subjecting unvulcanized india rubber under non-vulcanizing conditionsto the action of a small amount of a soft tacky heat reaction product of a rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked to phosphorus and a condensed polynuclear aromatic hydrocarbon for a time and temperature suflicient to decrease the resistance conditions to the action of a. small amount of a soft sticky heat reaction product of a natural be madewithout departing from the spirit of the rubber and substantial proportions based on the rubber of an aryl dichlor phosphine having the two chlorine atoms linked to phosphorus and a condensed polynu'clear aromatic hydrocarbon for a time and temperature suflicient to decrease the resistance of the rubber to flow over that which it would have in the absence of said soft sticky heat reaction product.

10. The method of increasing the plasticity or assess conditions to the action or a small amount oi a soft tacky heat reaction product or suayule rubber and substantial proportions based on the rubber of tolyi dichlor phosphine having the two chlorine atoms linked to phosphorus and retene for a time and temperature suflicient to decrease the resistance of the rubber to flow over that which it would have in the absence of said soit tacky heat reaction product.

ROBERT L. SIBLEY. 

